/Engine/Source/Runtime/GeometryCore/Public/Polygon2.h
Construct a normal at a vertex of the Polygon by averaging the adjacent face normals. This vector is independent of the lengths of the adjacent segments. Points "inward" for a Clockwise Polygon, and outward for CounterClockwise
[TVector2](API\Runtime\Core\Math\TVector2)< T > GetNormal_FaceAvg ( int VertexIndex ) const